Y Combinator is once again showing off their most recent early-stage startups at Demo Days this week, with companies offering varied solutions to problems on the web like metrics, content creation, hosting, polling, and even Internet connected appliances. But of all of Y Combinator’s promising startups, only CO2Stats showed a competent yet passionate desire to solve a world-wide problem using the power of the Web.

By power of the Web, I literally mean energy. CO2Stats hopes to leverage the growing energy consumption of the Internet to increase the demand for renewable energy.

Its founders, Alex Wissner-Gross and Tim Sullivan, claim that the Internet’s total carbon footprint is now larger than the entire aviation industry. C02Stats solution to this problem was to create a way for websites to purchase renewable energy credits to offset that large footprint.

The company is similar to VeriSign, in that their main public-facing element is a badge customers can place on their website. But instead of guaranteeing that the site is SSL secured, CO2Stats’ badge shows that the host site runs on green power credits. The badge goes far beyond simply branding a site to be “green,” and represents that the website is actually purchasing renewable power to offset the amount of energy being consumed by both their servers as well as their customer’s computers.

How does CO2Stats power web servers and the customers who visit them? Tim and Alex explained to me (and on their website) that the first step was to research and compile a world-wide database of geographic energy sources, a process that took six months. When someone surfs to a CO2Stats-badged website, scripts record the location of the user and match them to their corresponding geographic energy source in the database. For example, if a visitor is from Virginia, the database would register a coal-based energy user had visited the site. The scripts then details how long that person spent on the site, their total power dedicated to loading and browsing it, and even the approximate window size to estimate the monitor’s power consumption. That data is then run through the database and outputs a corresponding number of green power credits are purchased to offset the energy used by that individual. Clicking the badge will then display how many pounds of C02 are offset through the program.

In order to make a profit off this renewable energy market, CO2Stats purchases green power credits in bulk from Sustainable Travel International and NativeEnergy. Bulk purchases allow for a profit margin over the fixed monthly rates the CO2Stats charges based on total page views. A site can purchase the badge at a fixed monthly rate based on page views brackets (under 5 million, 1 million or 500k), while CO2Stats manages purchasing green credits required to offset the site.

Tim and Alex believe that renewable energy’s hope lies in being adopted by high-technology firms first, then trickle its way down to the average user. The badge method CO2Stats uses allows companies to purchase the renewable energy, while consumers and surfers can enjoy the peace of mind that their surfing is carbon-free.

More news, commentary, and predictions from The Industry Standard:

• News: Y Combinator Demo Day: CO2Stats, Posterous and others show their stuff
• News: Discover Your Solar Savings at Roofray
• News: Expanding green IT